Herbs contain active constituents. How an herb is prepared for therapy depends on which active constituent is needed. If you examine a plant chemically, it is composed of many components, and these components give an herb its biological activity. One component may be responsible for the primary activity of one herb, while a completely different component may be the active constituent in another. Herbs exert their effects because of these different chemical components. Although herbs have been used for centuries, many of the constituents responsible for their physiologic activity have only been identified in relatively recent times.
Phenols
Phenols are aromatic hydrocarbons consisting of six carbon atoms arranged in a ring (or multiple linked rings) with a hydroxyl group (–OH) attached. They are weakly acidic and soluble in water. An example of a phenol is acetylsalicylic acid, which is chemically related to aspirin. Phenols often act as anti-inflammatory agents and may also have antiseptic properties. In plants, one of the functions of phenols is protection against insects. A group of phenols known as salicylates is found in wintergreen and willow.
Volatile Oils
Volatile oils are commonly referred to as essential oils. They are complex substances and may contain as many as 100 different compounds. Monoterpenes, which are 10-carbon molecules, are the most common constituents of volatile oils. Menthol, extracted from peppermint and other members of the mint family, is an example of a monoterpene. Camphor, derived from Cinnamomum camphora, is another.
Flavonoids
Flavonoids are a class of water-soluble plant pigments found in fruits, vegetables, and certain beverages. They have antioxidant properties, meaning they help protect cells from damage caused by reactive chemicals known as free radicals. Studies have shown that flavonoid intake is inversely related to mortality from coronary heart disease and to the incidence of heart attacks.
Flavonoids can be classified into several categories, although there is some controversy regarding classification. One system divides them into isoflavones, anthocyanidins, flavans, flavonols, flavones, and flavanones. Well-known flavonoids such as genistein (found in soy) and quercetin (found in onions) are often discussed as specific subtypes within these categories. While flavonoids share structural similarities, their biological functions can differ significantly. Other flavonoids include hesperidin, rutin, citrus flavonoids, bilberry constituents, and many commonly used supplements.
Tannins
Tannins are bitter plant compounds that act as astringents. An astringent binds to and precipitates proteins and other organic compounds, including amino acids and alkaloids. The astringent effect of tannins is what causes the dry, puckering sensation in the mouth after consuming unripe fruit or red wine. Over time, the breakdown or modification of tannins plays an important role in fruit ripening and wine aging.
The term tannin comes from tanna, an Old High German word for oak or fir tree (as in Tannenbaum). The name reflects the historical use of tannins from oak wood in tanning animal hides into leather—hence the words tan and tanning.
Proanthocyanins
Proanthocyanins are closely related to flavonoids. They are pigments responsible for the coloration of flowers, fruits, and other plant parts. They are powerful antioxidants and may help protect cells from damage caused by free radicals.
Coumarins
The name coumarin comes from the French word coumarou, referring to the tonka bean. Coumarin has a sweet scent, often described as resembling freshly cut hay, and has been used in perfumes since the 19th century. It has also been used as a flavoring or aroma-enhancing agent in pipe tobacco and certain alcoholic beverages.
Coumarins are thought to be produced by plants as defense chemicals to deter insects. Different coumarins have different biological activities. Some coumarins found in horse chestnut contribute to effects on blood flow. Although coumarin itself does not have anticoagulant activity, it can be converted into the natural anticoagulant dicoumarol by certain species of fungi.
